IPsecVPNs-Juniper-SRX-技术文档

IPsecVPNsChapterTitleINTERNALUSEONLYIPsecVPNs2©2008JuniperNetworks,Inc.Allrightsreserved.TheMeaningBehindVPNsVPNsareusedtotransportprivatenetworktrafficoverapublicnetworkinfrastructure.ThetermVPNhasbeenusedbroadlyinthenetworkingindustryfordecades.Forinstance,thenetworkingindustryhasreferredtoX.25,FrameRelay,andATMinfrastructuresasVPNnetworks.AstheInternetspreadandascarriersandserviceprovidersmigratedalltheirserviceofferingstoIP,newformsofVPNsemerged.TypesofVPNsTodayWecansubdividethesenewformsofVPNsintothreecategories:•Clear-textVPNs:TheseVPNsincludeLayer3VPNs,Layer2VPNs(KompellaandMartiniimplementations),andvirtualprivateLANservice(VPLS).TheseVPNsrelyonMPLSservicesandtheuseofsignalingprotocolsoverIP.•SecureVPNs:TheseVPNsareIPsecVPNs,carryingpayloadoverIPsecurely.•Combinationofclear-textandsecureVPNs:TheseVPNsarebasedonLayer3VPNs,builtonMPLStechnology,andcompoundedwithIPsecsecurity.INTERNALUSEONLYIPsecVPNs©2008JuniperNetworks,Inc.Allrightsreserved.3SecureVPNsAnetworkdevicethatbuildssecureVPNsmustbeabletoperformthefollowingactions:•Encrypttheoriginalpacketsothatitcannotbeeasilydecodedshoulditbeinterceptedonthepublicnetwork;•Verifytheoriginalpayloadensuringdataintegrity;and•AuthenticatetheoriginatingdeviceasamemberoftheVPN,ratherthanarandomdeviceoperatingonthepublicnetwork.INTERNALUSEONLYIPsecVPNs4©2008JuniperNetworks,Inc.Allrightsreserved.SecurityConcernsTherearethreedrivingconcernsfornetworksecurity:confidentiality,integrity,andauthentication.•Confidentiality:Onlinebanking,creditcardinformation,oracompany’scompetitiveinformation—howdowekeepthisinformationsecurefromthemaninthemiddle?Wewanttheinformationtobestoredinsuchawaythatifsomeoneweretocapturethisdatagram,theinformationwouldappearmeaningless.•Integrity:Eventhoughtheinformationmightbesecureandhidden,meaningthatsomeonemightnotbeabletodetermineorunderstanditscontents,itcouldstillbepossibleforsomeonetochangeit.Someonecouldtweakbitstochangethedatafromwhatwasoriginallysentthroughthenetwork.Sohowdowemakesurethatifthedataiscompromised,theremotestationrecognizesthisfactandrefusestoprocesstheinformation?•Authentication:Howdoestheremotestationverifythattheinformationcamefromthedevicefromwhichitexpectedittocome?Youdonotwanttobecommunicatingandsendingcriticalinformationtothewrongrecipient!INTERNALUSEONLYIPsecVPNs©2008JuniperNetworks,Inc.Allrightsreserved.5Confidentiality—DataEncryptionThefirstofthethreeVPNsecurityconcernsisconfidentiality.Encryptionprovidesdataconfidentiality.Encryptionisthemethodoftakinguserdata—referredtoasplaintext—andconvertingitintounreadableorsecretdatacalledciphertext.Anencryptionalgorithmandkeys(stringsofbitsthatseedtheencryptionprocess)areappliedtothedata,resultinginciphertext.Toreversetheprocessanddecrypttheciphertext,youmustknowboththeencryptionalgorithmandencryptionkey.Youcandecryptencrypteddatainoneoftwoways:•Symmetrickeyencryption:Thismethodusesthesamekeyforbothencryptionanddecryption;and•Asymmetrickeyencryption:Thismethodusesaprivatekeyforencryptionandamathematicallyrelatedpublickeyfordecryption.Thecipherstrengthdependsonthekeysize;thelargerthekey,themoresecurethecipheroutput.Thetrade-offisinprocessingtime—largerkeysusemorecomputationalcyclestoencryptanddecrypt.INTERNALUSEONLYIPsecVPNs6©2008JuniperNetworks,Inc.Allrightsreserved.Confidentiality—SymmetricKeyEncryptionSymmetrickeyencryptionisthemoststraightforwardformofencryptionwiththeleastamountofoverhead.Itiscalledsymmetricbecausethekeyusedtoencryptthedataisthesamekeyusedtodecryptthedata.Thus,thesamekeymustbeknownonbothsidesofaconnection.Symmetrickeysizesrangefrom40bits–1024bits.Thesekeysareconsideredtobeveryfastastheyarenotverylong,andtheyarewidelyusedforbulkdataencryption.However,becausethekeymustbeknowntoboththesenderandthereceiver,keymanagementisaproblemwhenusingsymmetrickeys.ExamplesofsymmetrickeyencryptionincludeRivestCipher4(RC4),DataEncryptionStandard(DES),AdvancedEncryptionStandard(AES),andBlowfish.INTERNALUSEONLYIPsecVPNs©2008JuniperNetworks,Inc.Allrightsreserved.7PublicKeyEncryptionThepublic,asymmetrickeyencryptionmethodrequiresapairofmathematicallyrelatedkeys.Oneofthekeysiskeptsecretandknownonlytotheowner;thiskeyistheprivatekey.Theotherkeyiswidelydistributedandcanbeaccessedbyanyone;thiskeyisthepublickey.Youcanonlydecryptdataencryptedbytheprivatekeybyusingthecorrespondingpublickey,andviceversa.Thekeysaremathematicallyrelatedsuchthatitisalmostimpossibletoderiveonekeyoutofanother.Publickeysizesrangefrom512to2048bits.Becauseofthelargesize,thesekeysareextremelyslowandgenerallynotfeasibleforbulkdataencryption.However,publickeysarewidelyusedforuseranddeviceauthentication(forexample,digitalcertificates).Anexampleofpublic,asymmetrickeyencryptionisRSA.INTERNALUSEONLYIPsecVPNs8©2008JuniperNetworks,Inc.Allrightsreserved.IntegrityNowthatwehavethedataencryptedasittraversestheInternet,wemustensurethatthedataisnotmodifiedalongtheway.Eventhoughanovicehackermightnotbeabletocracktheencryptionalgorithmandkey,thehackercanstillwreakhavocbymodifyingbitsthatarebeingcarriedintheencryptedpayload.I